1. Field of the Invention
The present invention relates to a pressure control valve, and more specifically, to a pressure control valve in the form of a composite valve that includes a check valve incorporated in a valving element of the pressure control valve.
2. Description of the Prior Art
Conventionally, pressure control valves are frequently used in a refrigerating cycle of the vapor-pressure compression type. In a pressure control valve described in Japanese Patent Application Laid-open No. 2000-230650, for example, a coil spring that applies a force to enlarge the opening of a valve port to a valving element is formed of a shape-memory alloy. In this case, the valve opening can be restrained from becoming smaller than a given value, and the refrigerant pressure on the outlet side of a radiator can be prevented from increasing excessively. Thus, apparatuses that are located on the high-pressure side of the radiator and a supercritical refrigerating cycle of a compressor can be prevented from being damaged.
In a pressure control valve described in Japanese Patent Application Laid-open No. 2000-81157, a temperature sensor of a control valve body is situated in a first refrigerant passage that connects the outlet side of a radiator and the inlet side of an internal heat exchanger, and a second refrigerant passage that guides a refrigerant flowing out of the heat exchanger to the upper-stream side is formed in a casing body. Thus, a delay of temperature change in a closed space (control chamber) behind the refrigerant temperature change on the outlet side of the radiator can be lessened, so that the temperature response of the pressure control valve can be improved.
In a pressure control valve described in Japanese Patent Application Laid-open No. 2001-82835, a noncondensable gas and a refrigerant with given density are sealed into a closed space in order to lessen fatigue breakage of a joint between a diaphragm and a valving element. The diaphragm is displaced by the difference between the internal pressure of the closed space and the refrigerant pressure on the outlet side of a radiator through all the area from a supercritical area to a condensation area. By doing this, stress can be prevented from being concentrated on the joint between the diaphragm and the valving element.
In general, according to these conventional pressure control valves, check valves are frequently used in a refrigeration system. For ease of installation of the refrigeration system, it is to be desired that various valves including pressure control valves should be readily installed even in a narrow space. In view of the durability or maintenance of the pressure control valves or manufacturing costs, moreover, the valves should preferably be simple in construction.